This invention relates generally to a tool for punching a hole in the wall of an electric distribution transformer tank to remove a sample of oil therefrom without the necessity of deenergizing the transformer or removing the tank lid. More specifically, the invention relates to a transformer tank punch which is threadably insertable into an interiorly threaded hollow shaft in a conventional ground lug nut welded to the side of a transformer tank for removing a sample of oil from the tank through the tool itself by means of a suction device attached to the tool, the tool also providing a permanent seal for the hole punched in the tank and means for attaching a ground wire thereto to permanently ground the tank.
Some years ago, over a span of many years, a large number of electric distribution transformers were manufactured in this country for use by electric utilities in which the transformer coil and core were disposed in a steel tank filled with oil, which oil contained the now dreaded polychlorinated biphenyls known as PCBs. Since the devastating adverse effects of PCBs on human health have been confirmed, a nationwide cleanup effort is underway under federal government mandate.
Part of this effort involves the sampling and testing of oil contained in suspect electric distribution transformers currently in service or in place in this country which were manufactured and/or distributed during the time period when PCBs were in use in the electric utility industry. Those transformers found to contain PCB contamination in their cooling oil must be promptly removed from their location and the contaminated oil must be disposed of according to stringent EPA guidelines. The monumental task still lying ahead for the electric utility industry in this regard is staggering in its many aspects, one major aspect of which is the huge number of man hours of time that will be required for line crews to check the oil in each and every suspect transformer.
In the past, it has been necessary in many cases to de-energize each pole mounted distribution transformer to be tested so that the tank lid, upon which a high voltage primary feedthrough bushing is mounted, can be safely unbolted and removed from the top of the tank to permit access to the oil within the tank by a lineman either secured by a belt from the pole or standing in a carefully positioned bucket of a line truck. In such cases, since the lineman is operating around the primary bushing and the line leading from the bushing to the high voltage primary distribution circuit, that portion of the circuit in which the lineman might conceivably come into contact, must be de-energized before the lid can safely be unbolted and removed. Then, following sampling of the oil from the transformer tank, the lid must be secured back in place on the transformer tank and, if the oil is determined to be free of PCB contamination, the transformer must be re-energized. Otherwise, if the sample is found to be contaminated, the lid is replaced and the transformer is removed from the pole and from further service.
More recently, a gun containing a punch pin has been used to puncture a transformer tank in the air space above the oil level after which a pipette containing a manually compressible suction bulb is inserted into the puncture and down into the oil to remove an oil sample. Thereafter, the puncture is sealed using a resilient plug. Since the puncture must be made at a high level on the tank above the oil level, the worker is in dangerously close proximity to the primary circuit connected to the transformer. Moreover, the security of the resilient plug in maintaining integrity of the puncture seal over an extended period of years is questionable. Also, the violent effect of driving the puncture pin into the tank using an exploding shell exposes the worker to the possibility of contact of the pin with the energized transformer coil with the potential for disastrous results. Lastly, since some transformers under certain conditions may include a positive air pressure in the space above the oil relative to ambient, in such cases the worker could be exposed to rapid expansion of air mixed with oil expelled through the puncture which in the worst case could contain PCB and, in addition, hot or even boiling oil.
Now since many of the distribution transformers in any given electric utility service area will be free of any PCB contamination, it would be highly advantageous from the standpoint of the time required to take oil samples from these units, if the samples could be safely taken without having to unbolt and remove the tank lids and without the necessity of first de-energizing that portion of the high voltage primary circuit in which the lineman might conceivably come into contact during the lid removal activity, and without having to replace and secure the tank lid after the sample is taken and, finally, without having to re-energize the contamination free transformers after the oil samples have been obtained.
Even in the case of those transformers found to contain PCB contamination, it would be an enormous saving of time if the oil in the tank of such units could be safely sampled without the need to first de-energize the transformer, then unbolt and remove the lid to gain access to the oil, and then replace and secure the lid preparatory to bringing the transformer down off the pole. Moreover, it would also be advantageous to provide a relatively safe means for sampling oil from energized transformers by minimizing the risk of exposure to hot contaminated oil and explosion of the transformer assembly.
Generally speaking, devices for punching holes in liquid filled containers to remove some or all of the liquid have long been known in the prior art. See, for example, the tap for drawing kerosene from cans as disclosed in U. S. Pat. No. 552,408 issued to G. Barnes on Dec. 31, 1895. One disclosed example of the reference device is a handgun shaped unit having a central projecting pin surrounded by rotatable cutter elements. The pin is punched into a tin can and the device is rotated to cut a circular opening into which a threaded punch body is screwed so as to jam a rubber washer surrounding the punch body against the can wall around the hole. A screw plug is then adjusted to permit kerosene to flow from the can through the punch body and handle as desired. Obviously, the can can not be reused without the punch body being in place in the hole with the rubber washer tightly abutting the can wall around the hole to prevent leakage. This assembly, while suitable for manually punching a hole in a thin walled tin can and thereafter scribing or cutting a hole therein, is clearly unsuited for safely penetrating the heavy gauge steel wall of an electric distribution transformer tank.
Devices which permit the sampling of a fluid from within reaction vessels and other cylindrical containers with a needle syringe have also been known in the prior art. See U.S. Pat. No. 4,056,981 issued to J. Kalka et al. on Nov. 8, 1977 and U.S. Pat. No. 4,010,648 issued to R. J. Harris, Sr. et al. on Mar. 8, 1977. Both of these devices employ fittings which must be affixed to the container wall so as to communicate with the interior thereof, after which a needle syringe can be used to penetrate a seal in the fitting to access the fluid in the container. The use of such a resilient seal is not deemed satisfactory to seal a transformer tank over a term of years.
See also U.S. Pat. No. 4,809,735 issued to F. R. Volstadt et al. on Mar. 7, 1989 and U.S. Pat. No. 4,598,731 issued to D. G. Colson on July 8, 1986 which disclose two different types of screw-in-valve tapping devices for gas mains and high pressure water lines, the latter being a screw-in-type punch and the former being a screw-in-type fitting. Neither of these devices have the capability of providing a grounding assembly for attachment of a ground wire to ground a transformer tank after an oil sample has been taken. Moreover, both devices require special fittings attached to the gas or water lines before those lines are placed in use.
Lastly, see U. S. Pat. No. 3,915,192 issued to J. A. Skvarenina on Oct. 28, 1975 which discloses another type of piercing valve for connection to a puncturable conduit. The device also contains a resilient pad seal for the area being punctured to prevent leakage and a wrenchable nut on the rear end of an internally threaded cap member for permitting wrenchable rotation of the device to punch a hole in the conduit. This device also fails to provide means for attaching a transformer ground wire thereto to provide a permanent ground for a transformer tank once a liquid sample is removed therefrom. Moreover, as previously mentioned, the long term integrity of a resilient seal for a hole punched in a transformer tank is highly questionable.
By means of my invention, these and other difficulties encountered with such prior art devices are substantially overcome.